Method of forming heat exchanger tubing and tubing formed thereby

ABSTRACT

A method of forming tubing with integral fins oriented parallel to its length, and to a heat exchanger tube produced by such a method. The invention involves extruding a tube so that the tube has at least one internal longitudinal passage, an external surface having a cross-sectional shape in a plane transverse to the extrusion direction, and at least one integral fin parallel to the extrusion direction and extending in a direction away from the external surface of the tube. The tube may be one of a plurality of tubes assembled in parallel to a pair of manifolds, and such tubes are preferably oriented so that their integral fins are substantially parallel, with the fin(s) of a given tube extending toward an adjacent one of the tubes.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to heat exchangers, suchas those of the type used in air-conditioning systems. Moreparticularly, this invention relates to a heat exchanger tubeconfiguration that incorporates integral fins for transferring heat toand from the tube.

[0003] 2. Description of the Related Art

[0004] Heat exchangers are employed within the automotive industry ascondensers and evaporators for use in air conditioning systems,radiators for cooling engine coolant, heater cores for internal climatecontrol, etc. One type of heat exchanger construction used in theautomotive industry for condensers and evaporators comprises a number ofparallel tubes that are joined to and between a pair of manifolds,creating a parallel flow arrangement. The ends of the tubes aretypically metallurgically joined (brazed, soldered or welded) to tubeports, generally in the form of holes or slots formed in a wall of eachmanifold. In order to maximize the amount of surface area available fortransferring heat between the environment and a fluid flowing throughthe heat exchanger, automotive heat exchangers often have a tube-and-finconstruction in which numerous tubes thermally communicate with highsurface area fins. The fins are typically in the form of flat panelshaving apertures through which tubes with circular cross-sections areinserted, or in the form of sinusoidal centers that are positionedbetween adjacent pairs of “flat” tubes with oblong cross-sections. Ineither case, the resulting tube-and-fin assembly is oriented so that theedges of the fins face the fluid (e.g., air) flowing between the tubes,i.e., the fins are normal to the plane defined by the tubes of the heatexchanger.

[0005] Alternative forms of fins have been suggested, examples of whichinclude U.S. Pat. No. 4,546,819 to O'Connor, U.S. Pat. No. 4,951,742 toKeyes, and U.S. Pat. No. 5,353,868 to Abbott. Each of these patentsdiscloses a cooling tube whose outer surface undergoes a second formingoperation to have integral fins. Abbott discloses fin strips formed bylancing a conduit, while O'Connor and Keyes disclose integral finsformed by rolling the exterior of a tube. An approach to formingintegral fins on round plastic tubing is taught in U.S. Pat. No.4,926,933 to Gray, in which integral helical fins are defined on theexterior of a round plastic tube during injection molding or extrusionof the tube.

SUMMARY OF INVENTION

[0006] The present invention provides a method for forming tubing withintegral fins, and to a heat exchanger tube produced by such a method.The method generally involves extruding the tube through a die so thatthe tube has at least one internal passage extending in a longitudinaldirection parallel to the longitudinal direction in which the tube wasextruded, an external surface having a cross-sectional shape in a planetransverse to the extrusion direction, and at least one integral finparallel to the extrusion direction and extending in a direction awayfrom the external surface of the tube. As such, the one or more fins areparallel to the longitudinal axis of the tube. The tube can be one of aplurality of identical tubes assembled in parallel to a pair ofmanifolds, and such tubes are preferably oriented so that their integralfins are substantially parallel, with the fin(s) of a given tubeextending toward an adjacent one of the tubes. In this arrangement, thefins are oriented substantially parallel to the plane in which the tubeslie, contrary to conventional practice.

[0007] Significant advantages of the integral tube-and-fin constructionof this invention include the elimination of separate fin stock and thecostly manufacturing equipment associated with producing and brazingfins for heat exchanger tubing. Another feature of the invention is thepotential for reducing the size of a heat exchanger for a givenapplication as a result of the ability to more densely pack the tubes.Heat exchangers incorporating the integral tube-and-fin construction ofthis invention can find use in a variety of applications, includingautomotive and beverage cooling applications. For example, the integraltube-and-fin construction of this invention is suitable for use inconventional automotive cooling and air-conditioning units, as well ascondensers and evaporators for CO₂-based air-conditioning systems. Forbeverage cooling applications, the integral tube-and-fin constructionhas the potential to exhibit improved water shedding characteristics andgreater resistance to clogging by dirt, dust and other debris commonlyencountered by beverage coolers.

[0008] Other objects and advantages of this invention will be betterappreciated from the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is a perspective end view of an as-extruded tube withmultiple integral fins in accordance with this invention.

[0010]FIG. 2 is a perspective end view of the tube of FIG. 1 following asecondary operation in which portions of each fin are removed inaccordance with an embodiment of the invention.

[0011]FIG. 3 is a perspective view of an alternative fin configurationformed by bending portions of each fin in a secondary operation.

[0012]FIG. 4 schematically represents a process for forming the tube ofFIG. 2.

[0013]FIGS. 5 and 6 schematically represent individual steps of theforming process of FIG. 4.

[0014]FIG. 7 is a perspective end view of a two-piece manifold forassembly with the tubes of FIGS. 1 through 3.

[0015]FIG. 8 is a frontal view of a heat exchanger comprising multipletubes of the type shown in FIG. 2.

DETAILED DESCRIPTION

[0016]FIG. 1 represents a segment of an as-extruded heat exchanger tube10 configured in accordance with this invention. The tube 10 isrepresented as a flat (oblong cross-section) tube portion 12 withmultiple internal passages 14 that extend in a longitudinal direction ofthe tube portion 12. According to a preferred aspect of the invention,the tube 10 is extruded and the passages 14 are formed during theextrusion process so as to be parallel to the extrusion direction of thetube 10. The external surface of the tube portion 12 is defined byoppositely-disposed flat surfaces 16 and two oppositely-disposed lateralsurfaces 18. Multiple fins 22 extend from each of the flat surfaces 16in a direction normal to the flat surfaces 16 and parallel to theextrusion direction. The fins 22 on one of the surfaces 16 are shown asbeing staggered relative to the fins 22 on the opposite surface 16,though such a configuration is not required.

[0017] As disclosed and defined herein, the fins 22 are “integral fins”with the tube portion 12 in that they are features formed of materialcontinuous with the material that forms the tube portion 12, and notformed of material subsequently attached or otherwise added to the tubeportion 12. In a preferred embodiment, the fins 22 are formedsimultaneously with the tube portion 12, i.e., during the extrusionprocess, though integral fins 22 could also be defined following theoperation by which the tube portion 12 is formed by deforming thesurface of the tube portion 12 to create the fins 22.

[0018]FIGS. 2 and 3 depict, respectively, a tube 20 and a portion of atube 20 formed by performing secondary operations on the tube 10 ofFIG. 1. The tube 20 in FIG. 2 is depicted as having a relatively shortlength, though any length of tube is within the scope of this invention.In each case, the secondary operation has resulted in each fin 22 havingalternating edge portions 24 and 26 along its length and terminalportions 28 spaced a longitudinal distance from each end of the tubeportion 12. As depicted in FIGS. 2 and 3, the edge portions 24 extend agreater distance from the surfaces 16 of the tube portion 12 than theedge portions 26. In FIG. 1, the edge portions 26 are defined by theremoval of rectangular sections from the edges of the fins 22, while inFIG. 2 the edge portions 26 are defined by bending over rectangularsections along the edges of the fins 22. In either case, the edgeportions 26 define a longitudinal gap between adjacent edge portions 24,creating a profile similar to a square sawtooth. While the sectionsremoved and bent in FIGS. 2 and 3, respectively, are rectangular inshape, various other shapes are possible.

[0019]FIG. 4 schematically represents a process for forming the tube 10of FIG. 1 and performing a skiving operation to form the tube 20depicted in FIG. 2. The tube 10 is shown as being extruded with a die 30having an appropriate shape to produce the desired integral tube-and-finform shown in FIG. 1. Following extrusion, the tube 10 is passed througha pair of sizing rollers 32 before entering a skiving die 34, both ofwhich are shown in more detail in FIGS. 5 and 6 respectively. The sizingrollers 32 are intended to improve the form and finish of the tube 10following extrusion, and for this purpose include individual rollersthat travel the flat surfaces 16 of the tube portion 12 between fins 22.The skiving die 34 is depicted as having multiple 36 into which skivepunches 38 (only one of which is shown) are actuated to engage the fins22 of the tube 10, thereby removing the rectangular sections to definethe alternating shorter and longer edge portions 24 and 26 along theedges of the fins 22. To facilitate the skiving operation, the tube 10is preferably fed from a separate source (e.g., a roll of the tube 10)instead of directly from the extrusion process, so that the tube 10 canbe advanced into the skiving die 34 and then held stationary during theskiving operation. The skiving die 34 includes channels 40 thatfacilitate clearing of the rectangular sections removed from the fins22. As an alternative to material removal, the skive punches 38 can beconfigured to deform the rectangular sections to produce the tubeconfiguration shown in FIG. 3. After the skiving operation, the tube 10continues on to a die 42 where individual tubes 20 are cut from the tube10.

[0020] The tube 10 (and therefore the tubes 20) is preferably formedfrom a suitable aluminum alloy, though other alloys could be used. Thetubes 20 are attached, such as by brazing or soldering, to a pair ofmanifolds so that the tubes 20 are fluidically connected to themanifolds to allow fluid flow to and from the manifolds. The manifoldscan be of any suitable configuration for the intended application. FIG.7 represents a particular embodiment for a manifold 50 suitable forassembly with the tubes 20 of this invention. The manifold 50 is shownto have a two-piece construction comprising a base profile 52 and a cladsheet 54, the latter of which carries a brazing material and preferablya flux coating (not shown) for brazing the tubes 20 and the clad sheet54 to the profile 52. The base profile 52 is generally flat with aplurality of fluid passages 58, and therefore has a configurationsimilar to a flat heat exchanger tube, e.g., the tube portion 12 of thetubes 10 and 20 in FIGS. 1 through 3. Transverse slots 60 are machinedin one wall 56 of the profile 52 to permit assembly of the tubes 20 withthe profile 52 by inserting the ends of the tubes 20 into the slots 60.The base profile 52 includes oppositely-disposed tabs 62 for clinchingthe edges 64 of the sheet 54, by which the clad sheet 54 can bemechanically secured to the profile 52. The clad sheet 54 has openings66 corresponding in size, shape and location to the slots 60 in theprofile 52. In this manner, the clad sheet 54 can be mechanicallysecured to the profile 52 with the tabs 60 so that the openings 66 arealigned with the slots 60, and together the slots 60 and openings 66define ports for the tubes 20.

[0021]FIG. 8 depicts a heat exchanger 70 in which a number of the tubes20 are assembled with a pair of manifolds 50 of the type depicted inFIG. 7. The ends of the tubes 20 are received in ports 76 in walls 74 ofthe manifolds 50. Based on the manifold construction of FIG. 7, theports 76 are formed by the slots 60 and openings 66 in the profile 52and cladding sheet 54, respectively, and the walls 74 of the manifolds50 are formed by the joining of the cladding sheets 54 to the walls 56of the profiles 52. As shown in FIG. 8, the terminal portions 28 of thefins 22 of each tube 20 abut the wall 74 of the manifolds 50, such thatthe terminal portions 28 advantageously serve as tube stops during theassembly process. The tubes 20 are oriented so that their flat surfaces16 are normal to the plane defined by the tubes 20, with the result thatthe integral fins 22 of the tubes 20 are parallel to each other and tothe plane defined by the tubes 20, and extend toward an adjacent tube20. By spacing the longer portions 24 of each fin 22 a consistentdistance apart, the longer and shorter portions 24 and 26 of the fins 22can be aligned to create passages 72 within the heat exchanger 70through which a fluid (e.g., air) flows for heat transfer with the tubes20.

[0022] While the invention has been described in terms of particularembodiments, it is apparent that other forms could be adopted by oneskilled in the art. For example, the processing steps could be modified,and materials and tube and manifold configurations other than thosenoted above could be adopted in order to yield a heat exchanger suitablefor a wide variety of applications. Accordingly, the scope of theinvention is to be limited only by the following claims.

1. A method comprising the step of extruding a heat exchanger tube in anextrusion direction through a die so that the tube has at least oneinternal passage extending in a longitudinal direction parallel to theextrusion direction, an external surface having a cross-sectional shapein a plane transverse to the extrusion direction, and at least oneintegral fin parallel to the extrusion direction and extending in adirection away from the external surface of the tube.
 2. A methodaccording to claim 1, wherein the external surface has twooppositely-disposed flat surfaces and two oppositely disposed lateralsurfaces, and the cross-sectional shape of the tube is oblong as aresult of the flat surfaces having larger cross-sectional dimensionsthan the lateral surfaces.
 3. A method according to claim 2, wherein theat least one integral fin comprises a plurality of integral fins, andall of the integral fins are present on the flat surfaces of the tube.4. A method according to claim 1, further comprising the step ofperforming an operation on the at least one integral fin so that the atleast one integral fin has alternating first and second portions, thefirst portions extending a greater distance from the external surface ofthe tube than the second portions.
 5. A method according to claim 4,wherein the operation comprises selectively bending regions of the atleast one integral fin to form the second portions thereof.
 6. A methodaccording to claim 4, wherein the operation comprises selectivelyremoving regions of the at least one integral fin to form the secondportions thereof.
 7. A method according to claim 4, wherein theoperation comprises actuating punches in a direction normal to thelongitudinal direction of the tube to engage the at least one integralfin and define the first and second portions thereof.
 8. A methodaccording to claim 1, further comprising the step of removing a portionof the at least one integral fin from the tube adjacent an end of thetube, wherein as a result the integral fin has a terminal portion alongitudinal distance from the end of the tube.
 9. A method according toclaim 8, further comprising the step of assembling the tube with amanifold by inserting the end of the tube through a port in a wall ofthe manifold, the end of the tube being inserted through the port untilthe terminal portion of the at least one integral fin abuts the wall ofthe manifold, the longitudinal distance between the terminal portion andthe end of the tube establishing the extent to which the end of the tubeprojects into the manifold.
 10. A method according to claim 9, whereinthe tube is one of a plurality of tubes formed by the extruding step,the method further comprising the step of performing an operation oneach of the tubes so that the at least one integral fin of each tube hasalternating first and second portions and the first portions extend agreater distance from the external surface of each tube than the secondportions thereof, and the assembling step comprises inserting ends ofthe tubes through ports in the wall of the manifold so that the firstportions of the tubes are aligned with each other and the secondportions of the tubes are aligned with each other to define passagesbetween the tubes.
 11. A method according to claim 9, wherein themanifold is formed to have an external surface with an oblongcross-sectional shape and comprises two oppositely-disposed flatsurfaces, one of the flat surfaces defining the wall of the manifold inwhich the port is present.
 12. A method according to claim 11, whereinthe wall of the manifold is formed by brazing a cladding sheet to a baseprofile in which an internal passage is defined the base profile havinga slot and the cladding sheet having an opening that together define theport in which the end of the tube is inserted.
 13. A method comprisingthe steps of: extruding heat exchanger tubing in an extrusion directionthrough a die so that the tubing has multiple internal passagesextending in a longitudinal direction parallel to the extrusiondirection, an external surface having an oblong cross-sectional shapedefined by oppositely-disposed flat surfaces and two oppositely-disposedlateral surfaces, and multiple integral fins on the flat surfaces,parallel to the extrusion direction, and extending in directions normalto the flat surfaces of the tubing; performing an operation on theintegral fins so that each of the integral fins has alternating firstand second portions, the first portions extending a greater distancefrom the flat surfaces of the tubing than the second portions;separating the tubing into a plurality of tubes so that each of theintegral fins of each tube has oppositely-disposed terminal portionsspaced longitudinal distances from oppositely-disposed ends of the tube;and assembling the tubes with manifolds by inserting the ends of thetubes through ports in walls of the manifolds, the ends of the tubesbeing inserted into the ports until the terminal portions of theintegral fins abut the walls of the manifolds, the longitudinaldistances between the terminal portions and the ends of the tubesestablishing the extent to which the ends of the tubes project into themanifolds.
 14. A method according to claim 13, wherein the integral finsare present exclusively on the flat surfaces of the tubing and the tubesare assembled with the manifolds so that the integral fins of the tubesare substantially parallel and the integral fins of each of the tubesextend toward an adjacent one of the tubes.
 15. A method according toclaim 13, wherein the operation comprises selectively bending regions ofeach of the integral fins to form the second portions thereof.
 16. Amethod according to claim 13, wherein the operation comprisesselectively removing regions of each of the integral fins to form thesecond portions thereof.
 17. A method according to claim 13, wherein theoperation comprises actuating punches in a direction normal to thelongitudinal direction of the tubing to engage the integral fins anddefine the first and second portions thereof.
 18. An extruded heatexchanger tube having at least one internal passage extending in alongitudinal direction parallel to an extrusion direction of the tube,an external surface having a cross-sectional shape in a plane transverseto the extrusion direction, and at least one integral fin parallel tothe extrusion direction and extending in a direction away from theexternal surface of the tube.
 19. An extruded heat exchanger tubeaccording to claim 18, wherein the external surface of the tube has twooppositely-disposed flat surfaces and two oppositely-disposed lateralsurfaces, and the cross-sectional shape of the tube is oblong as aresult of the flat surfaces having larger cross-sectional dimensionsthan the lateral surfaces.
 20. An extruded heat exchanger tube accordingto claim 19, wherein the at least one integral fin comprises a pluralityof integral fins, and all of the integral fins are present on the flatsurfaces of the tube.
 21. An extruded heat exchanger tube according toclaim 18, wherein the at least one integral fin has alternating firstand second portions, the first portions extending a greater distancefrom the external surface of the tube than the second portions.
 22. Anextruded heat exchanger tube according to claim 21, wherein the secondportions of the at least one integral fin are defined by bent regions ofthe at least one integral fin.
 23. An extruded heat exchanger tubeaccording to claim 21, wherein the second portions of the at least oneintegral fin are defined by removed regions of the at least one integralfin.
 24. An extruded heat exchanger tube according to claim 18, whereinthe at least one integral fin has a terminal portion a longitudinaldistance from the end of the tube.
 25. An extruded heat exchanger tubeaccording to claim 24, wherein the tube is assembled with a manifoldwith the end of the tube residing in a port in a wall of the manifoldand the terminal portion of the at least one integral fin abuts the wallof the manifold.
 26. An extruded heat exchanger tube according to claim25, wherein the tube is one of a plurality of extruded heat exchangertubes assembled with the manifold, each tube having at least oneinternal passage extending in a longitudinal direction parallel to anextrusion direction of the tube, an external surface having across-sectional shape transverse to the extrusion direction, and atleast one integral fin parallel to the extrusion direction and extendingin a transverse direction away from the external surface of the tube,the at least one integral fin of each tube having alternating first andsecond portions, the first portions extending a greater distance fromthe external surface of the tube than the second portions, the firstportions being aligned with each other so that passages between thetubes are defined by the second portions.
 27. An extruded heat exchangertube according to claim 25, wherein the manifold is formed to have anexternal surface with an oblong cross-sectional shape and comprising twooppositely-disposed flat surfaces, one of the flat surfaces defining thewall of the manifold in which the port is present.
 28. A heat exchangerhaving a pair of manifolds and extruded tubes fluidically connected tothe manifolds to allow fluid flow to and from the manifolds through thetubes, each of the tubes comprising: multiple internal passagesextending in a longitudinal direction parallel to an extrusion directionof the tube; an external surface having an oblong cross-sectional shapedefined by oppositely-disposed flat surfaces and two oppositely-disposedlateral surfaces; and multiple integral fins on the flat surfaces,parallel to the extrusion direction, and extending in directions normalto the flat surfaces of the tube, each of the integral fins havingalternating first and second portions and oppositely-disposed terminalportions spaced longitudinal distances from oppositely-disposed ends ofthe tube, the first portions extending a greater distance from the flatsurfaces of the tube than the second portions; wherein the tubes areassembled with manifolds with the ends of the tubes residing in ports inwalls of the manifolds and the terminal portions of the integral finsabutting the walls of the manifolds, the tubes being oriented so thatthe integral fins of adjacent pairs of the tubes are substantiallyparallel and the integral fins of each of the tubes extend toward anadjacent one of the tubes.
 29. A heat exchanger according to claim 28,wherein the integral fins are present exclusively on the flat surfacesof the tubes.
 30. A heat exchanger according to claim 28, wherein thesecond portions of the integral fins are defined by bent regions of theintegral fins.
 31. A heat exchanger according to claim 28, wherein thesecond portions of the integral fins are defined by removed regions ofthe integral fins.